Have You tried to restart the server/server machine?
It's somewhat strange - this was an issue with the first releases of FMS 13 when the server was running for quite a while (and we have that/kind of that with older FMS, but I thought that the issue was solved in 13.02 or 13.03. If it reappered, an issue report should be written (forums.filemaker.com)
COuld be an installing problem as well. If nothing helps, the server meets the requirements, no other tasks are running, needed ports are open, firewall deactivated (et all), a deinstllation/reinstallation could be helpfull. Since the admin-window appears, java seeme to be OK (but a port problem could be the reason, whatever)
I will try to restart and see what happens . I installed FM server 14 just 2 weeks ago . Was working well till now.